Modern radiation therapy techniques include the use of Intensity Modulated Radiotherapy (“IMRT”), typically by means of an external radiation treatment system, such as a linear accelerator, equipped with a multileaf collimator (“MLC”). Use of multileaf collimators in general, and an IMRT field in particular, allows the radiologist to treat a patient from a given direction of incidence to the target while varying the shape and dose of the radiation beam, thereby providing greatly enhanced ability to deliver radiation to a target within a treatment volume while avoiding excess irradiation of nearby healthy tissue. However, the greater freedom that IMRT and other complex radiotherapy techniques, such as volumetric modulated arc therapy (VMAT), where the system gantry moves while radiation is delivered, and three dimensional conformal radiotherapy (“3D conformal” or “3DCRT”), afford to radiologists has made the task of developing treatment plans more difficult. As used herein, the term radiotherapy should be broadly construed and is intended to include various techniques used to irradiate a patient, including use of photons (such as high energy x-rays and gamma rays) and particles (such as electron and proton beams). While modern linear accelerators use MLCs, other methods of providing conformal radiation to a target volume are known and are within the scope of the present invention.
Several techniques have been developed to create radiation treatment plans for IMRT or conformal radiation therapy. Generally, these techniques are directed to solving the “inverse” problem of determining the optimal combination of angles, radiation closes and MLC leaf movements to deliver the desired total radiation close to the target, or possibly multiple targets, while minimizing irradiation of healthy tissue. This inverse problem is even more complex for developing arc therapy plans where the gantry is in motion while irradiating the target volume. Heretofore, radiation oncologists or other medical professionals, such as medical physicists and dosimetrists, have used algorithms to develop and optimize a radiation treatment plan.
When executing a radiation treatment plan using an external-beam radiation treatment system, it is possible that certain field geometries may cause machine-to-machine or machine-to-patient collisions. In such cases, automated execution of the treatment plan may need to be prevented or else accidents may occur. Therefore, it may be desirable to evaluate collision possibilities when planning and delivering a radiation treatment to ensure the safety and usability of a radiation treatment plan.